texts: What was the composition of the primordial asteroid belt?

texts: According to one theory, the region between Mars and Jupiter was once populated by several primordial planets with a combined mass of roughly the earth.  These planets provided the material that made up the original asteroid belt.  Since then, 99.9% of this material was lost.  The current composition of the asteroid belt is about 10% metallic and 90% silicate/carbonaceous.  Could we assume that the original asteroid belt had the same composition?  Or, at least a very similar composition?


texts:
I dug up my old 6" Dobsonian telescope from storage and the mirror looks like the following:

The picture is down the tube, so you can see the spider holding the secondary. To my eye, the spots look like corrosion and not cleanable, but does anyone actually know what they are?

It was stored relatively carefully - not totally sealed but in a house, with the tube covered with a plastic bag. So huge temperature changes are not likely, but it does quite humid here. It was last in action > 10 years ago.

The only other thing I know about the scope is that it was made by Criterion, sometime before the 1980s.


texts: Can a probe orbit Pluto given Charon's gravity?

texts: Is it possible for a man-made probe to orbit Pluto given its closeness to Charon? The gravitational field interaction of Pluto and Charon is likely to make simple orbit structure difficult for a man-made probe. Thanks for your insight.


texts: What might be the cause of the hot summer on Earth in 2018?

texts:
I have a question relating to the hot temperature this summer. There are 3 reasons that I can come up with:

Chemical, greenhouse effect.
Increased solar activity.
Orbital Resonance. The Earth is closer to the Sun, due to gravitational pull from other planets.

Anybody know something about Orbital Resonance? The orbits are affected by one another as they line up? Particularly the larger ones like Jupiter, Neptune and Saturn?


texts: Astronomy is new to me so my question might be stupid: I read that a nautical mile is defined as one minute of latitude along any line of longitude. What if it was the other way round, i.e. one minute of longitude along any line of latitude? Would it make any difference?


texts:
I am teaching myself astronomy and I'm working on a basic problem regarding time dilation around black holes.

The question is basically this: if a neutron were ejected from a nucleus at a distance of 3km from a 1 solar mass black hole, how long would it appear to take for the neutron to decay (the assumption here is that the neutron would decay in 15 minutes... right on the half-life) to an outside observer?

My first thought was that we'd never see it decay, because 3km is the Schwarzschild radius of a BH of that mass, so the frequency would basically be $0$ and we'd never observe the decay event.

The text notes the time dilation

$$
\frac{\Delta t'}{\Delta t_\text{obs}} = \frac{\nu_f}{\nu_i}$$
where $\Delta t'$ is the the time difference between two events at the source and $\Delta t_{obs}$ at the observer.

We can use the relativistic red shift equation to get the wavelength difference (9.2 in my case using 1 solar mass and a radius of 3km) so that wouldn't be infinite, just big. For a 15 min $\Delta t'$ then, the $\Delta t_{obs}$ would be 15 min * 9.2, yeah?

So my two answers obviously contradict each other. What am I missing in my approach here?


texts: Which are the best American universities/colleges for observational astronomy?

texts:
I'm a French student and I'm planning to go to the United States for a graduate program in astronomy.

When I will arrive in the U.S. I will begin by the first year of graduate. Then I will pursue with a Ph.D. and some postdoctoral research.

I would like to know which are the best American universities/colleges for what I want to do.

Concerning what division of astronomy I am interested in:
I'm not interested in the conception of telescopes, instruments and other systems. I'm not interested in engineering. And I'm not interested in extremely theoretical astronomy either.
I'm interested in observational astronomy.

Regarding what subfields of astronomy I am interested in:
I'm not interested in extragalactic astronomy or cosmology.
I'm interested in planetary astronomy, exoplanetology, exobiology, SETI, stellar astronomy in the solar neighborhood.
I'm not interested in things that are less than 2 Astronomical Units or more than 70 light years away from us.


texts: Did we ever witness a "meteor shower" which was actually dust or debris of some kind from our own Moon?


texts: Why is dark energy density given in grams per cm$^3?$

texts:
According to Wikipedia article,

  The density of dark energy ($~ 7 × 10^{−30} g/cm^3$) is very low, much less than the density of ordinary matter or dark matter within galaxies. However, it comes to dominate the mass–energy of the universe because it is uniform across space.

Other sources I found also give the density either as percentage of mass of the universe, or just as mass density like above, $kg/m^3$ or similar.

In about all other applications and contexts of usage of energy density, I'd find MJ/L, or other units of energy per volume. Why is energy of density given as mass per volume, and how do I convert it to more familiar units? Using $E=mc^2$ ?


texts: How can astronomers pinpoint the location of the source of a neutrino?

texts:
In the popular press, in recent months, we have heard a lot about high-energy neutrinos from far outside our solar system reaching our detectors....
But I wonder...
If a single neutrino from a great distance randomly, rarely, smacks a xenon atom in a detector, how the heck can they 'triangulate' it's direction?


texts: I've been viewing Google Sky, which is quite amazing, and came across a rather expansive rectangle where no stars are visible at 22h13m04.44s   4°59'29.49" (see image below). My only thought is that there's probably a satellite or something up there that Google is required to hide. Any thoughts on what this is?


texts: Given sunrise, noon, sunset, longitude and latitude can I calculate the "hight" or "ascension" of the sun?

texts:
I'm trying to make a simple app for my own use to be able to check which of my favorit restaurants have outdoor seating sun and for how long etc.

Given the data in the title (sunrise, noon, sunset, longitude and latitude) I can draw a path where the sun should be at any given time, but I want to display the hight as well.

I live in sweden where the sun changes "hight angle" (sorry I don't know the exact term for it) which make the angle relevant when deciding on seatings amongst high buildings.
My end goal is to be able to use google maps 3D data to actually cast shadows on the map in a realistic way!

I have no Idea if I'm in the right place but I figure I'll give it a shot :)


texts: Is the discovery of Alien or Extra Terrestrial Life a function of the science of Astronomy? When i read astronomy articles on the search for new Planets or discussions on Mars a lot of the topic is on the planets occurring in the habitable zone and the possibility of life on them or stories on the possibility of previous life on Mars. Is this actually part of the science objectives for the Astronomy community, or is there another branch of science who is tasked with this? Is Astronomy only focused on the mechanics of celestial bodies and the discovery of Alien or Extra Terrestrial life is just and interesting sidebar?


texts: Python interface for DMK 23U274 USB camera for astrophotography

texts:
I have access to a monochrome USB camera (DMK 23U274, The Imaging Source) and I'd like to record focal plane images from a small telescope with a python script that would control it by setting exposure times and triggering image captures.

Ideally I would like to be able to do this running on a Windows or MacOS laptop or a Raspberry Pi running Raspbian Linux but I don't know if that would require three different sets of special software in the middle (dll's or whatever).

Are there any platform-agnostic ways of doing this via USB? If not, are there Python solutions for amateur astronomers that can run on one or two of these platforms at least?

The only thing that I have found is this, but it specific to Windows and it seems to be an unfinished Python wrapper with unresolved memory leak issues:

https://github.com/TheImagingSource/IC-Imaging-Control-Samples/tree/master/Python
https://github.com/TheImagingSource/IC-Imaging-Control-Samples/issues/7

update: I've also found the following "Python wrapper for the IC Imaging Control SDK from The Imaging Source (TIS)" which "only works on Windows due to wrapping a DLL" so my hope for a platform-agnostic Python package is waning.

https://github.com/morefigs/py-ic-imaging-control


texts:
I hope this is the right place to ask this question, and I apologise if not.

I've come across a date written in an old book, but it is written using what seems to be a lunar/zodiac system.
Below is a picture of the date (ignore the text above it):

I'm trying to work out what this date would have been in our modern calendar, but I can't seem to find any tables or almanacs that go back that far.

Are there any publicly available tables that do go back to 1587? If not, how exactly could I go about calculating the answer for myself? I am a mathematician, so a bit of wacky maths should be within my capabilities.
This is the answer I'm probably expecting from this site: some kind of program/algorithm/formula to be able to work out on what date the moon would have been in Taurus in

If not, any ideas as to where best for me to ask/look next?


texts: Any observed example of a planet hitting its parent star?

texts: I did some research and a likely candidate is hot Jupiter type migration where the orbit didn't stabilize and crashed into the parent star.


texts: Will JWST be as durable as the hubble telescope?

texts:
JW Space Telescope is designed for a 5-10 year mission duration. Seeing as Hubble and other space missions have paved the way for JWST for reliability issues, It even has zero friction gyro's with 100+ years mean time before failure. Is it reasonable to think that JWST can last longer than Hubble?

JWST will orbit a Lagrange point in earth's shadow and will be 4 times further than the moon, around 10 days of travel away, and NASA states that JWST won't be serviceable. Why?

Why are JWST's fuel limitations so short? Are there no provisions for refueling? even a refueling craft? How many gallons of dinitrogen tetroxide ($N_2O_4$) as oxidizer and hydrazine ($N_2H_4$) will it contain?

Surely NASA are secretly hoping for a 20 year mission?


texts:
update: I still haven't been able to get my hands on the Icarus paper linked below (I'll try other libraries) but these are newer and quite interesting!:

Constraining the thickness of polar ice deposits on Mercury using the
Mercury Laser Altimeter and small craters in permanently shadowed
regions
nvestigating Mercury’s South Polar Deposits: Arecibo RadarObservations and High-Resolution Deter minationof Illumination Conditions

How did Arecibo make radar images of ice on Mercury's poles?

How were observations of the poles of Mercury geometrically possible from Earth?
How was "high-resolution (1.5-km) imaging" possible from Earth?
How was ice identified and imaged?

From Chapter 6; Planetary Radar Astronomy in A Strategy for Active Remote Sensing Amid Increased Demand for Radio Spectrum (2015):

Radar observations from Earth continue to provide new information about the terrestrial planets and the Moon despite the many spacecraft flybys, orbiters, and landers. The unique radar back-scattering properties of water ice led to the discovery by ground-based radar of ice deposits in the permanently shadowed portions of impact craters at Mercury’s poles. High-resolution (1.5 km) radar imaging of these deposits has mapped out their distribution with high precision9 (Figure 6.9).
9Radar imagery of Mercury’s putative polar ice: 1999–2005 Arecibo results Icarus, 211, (1) January 2011, pp 37-50

FIGURE 6.9 Arecibo radar image of the distribution of ice deposits at the north pole of Mercury (yellow), superimposed on a mosaic of Messenger orbiter images showing the coincidence of the ice deposits with the shadowed portions of impact craters. SOURCE: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.


texts: Does binarity play a role in spectral fitting?

texts:
Most of the spectroscopic surveys like SDSS classify stars into one pure spectral type.

However, a large fraction of stars are in binaries.

Can we know whether a spectral fitting is good enough? Is there something like $\chi^2$?

In other words, is it possible we can estimate the probability that a star is in a binary based on one spectrum?


texts: Why don’t we feel the Earth rotating beneath us?

texts:
I’m not sure all of the details in the experiment but basically it went as follows. Someone marked their location of take off in a hot air balloon and went straight up in the air. They stayed suspended for some time before coming straight back down. Apparently the result was that they had not drifted from the original take-off point underneath them. Maybe I got all of that incorrect, but I’m sure it’s close.

But if in that experiment the Earth had no effect on the landing point, why does the “rotation of the Earth” need to be factored into making the shot with a long range rifle for example? Now I know it isn’t the best comparison and that there are many different factors in both scenarios. Such as “the bullet is traveling and in the experiment the balloon wasn't”, but I’d just like to hear different theories and opinions as to why this is.

P.S. I know a popular answer is going to be that the Earth is too massive for us to feel its spin, but I’m thinking deeper than that!


texts: Could an object block out the Sun from Earth's view for 3 hours?

texts: how large, massive, far away (from earth), and fast would an object (planet-like) have to be to block out the Sun for 3 hours and not disturb Venus, Earth, or the Moon?


texts: I from India saw various stars moving in a line from North-West direction to the South-East direction at 5:27 AM on date 13 february 2020... They all are moving rapidly and can be easily seen from the earth's surface.... Wat was it? Any idea? Any one?


texts: Changes of the velocity of the Moon due to impacts from other objects?

texts:
Has the moon’s velocity changed since ‘shortly’ after it’s formation due to impacts?

Wouldn't it be likely that a significant collision would have occurred over such a long period of time?

It would seem an object with enough momentum to change the velocity of the Moon would have made an impact on its velocity at some point over the millennia.


texts: Solar Wind and Asteroid orbital behavior

texts:
Can the solar wind affect the orbital elements of a nearby asteroid?

I would like to know if solar activity has an effect on the asteroid's orbit or gravitational stability and or can cause a gravitational disturbance to a meteoroid near the earth.


texts: Is the Earth going to evolve towards Mars' fate or Venus' fate?

texts:
Upon reading on this site (and many others), one can think that Mars might have supported life in a distant past (discovery of liquid water, valleys, mountains...).

On the other hand, Venus is the perfect example of the consequences of the greenhouse effect. A planet where life is simply impossible because no heat can escape the planet's ultra-thick, CO2 filled atmosphere.

So, with a lot of exageration, one can say that both Mars and Venus could be the Earth's distant future.

Since the Earth is actually facing global warming and greenhouse effect, I was wondering if the Earth would one day be like Venus ? Or if it is going to be like Mars, with no more magnetosphere and almost no atmosphere left ?
Or if it is not going anywhere near those two planets' fate ?


texts: who use the GADGET-2 pack for simulation? can I do it with my PC?

texts:
I want to do hydrodynamic simulatin for universe at vary redshifts. How can I do it?
or how can I find an simulation of universe for use my work?


texts: Is the NASA solar dynamics website offline? If not how can the daily sun 'movies' be downloaded from https://sdo.gsfc.nasa.gov/data/dailymov.php?


texts: Are all the photos of the universe really so colorful or is it just visual effects that are added later?

texts: Do the colorful pictures of the universe show how it looks like that in reality or is it just a visual effect that is added later.


texts: Diameter of the moon from the diameter seen in the telescope

texts:
I'm reading a chapter on convex lenses and it has this diagram:

The chapter explains that triangles ABC and ADE are similar. Thus, ratio of CB to DE is equal to the ratio of BA to AD.
Does this mean that

if I look at the moon in the telescope that is 1 m long,
and the moon appears to be (I will make up a number) 1 cm in diameter,
knowing that the distance between moon and Earth is 384,000 km,

I can conclude that the moon is 3,840,000 m in diameter?
This is coming from 384,000 km / 1 m = X / 1 cm or, when converted to meters, 384,000,000 / 1 = X / 0.01


texts: Scholarly work on the gravitational disruption of a rocky planet by a close pass with another planet?

texts:
note: While the apparently abandoned question Effects of a rogue planet passing between the Earth and the Moon? (inspired by Thundarr the Barbarian) asks for speculation and was answered with it, this question asks for something different. Solar system evolution will likely involve both accumulation of matter into planets and destruction of formed planets by various mechanisms.
I'm interested in finding out if there is scholarly work on the *gravitational disruption of rocky, Earth-like planets due to close passes by, but not collisions with other planets.

An earth-sized rogue planet passing at high speed on a hyperbolic orbit around the sun will generally not have a huge effect on the solar system as a whole.  But if it did happen to pass close to earth (say ~1 million miles), it could seriously disrupt the Earth's orbit around the Sun and the Moon's orbit around the Earth.  Most perturbations would lead to much more elliptical orbits.  These would likely lead to an increase in seasonal extremes and perhaps to larger ocean tides.  These changes would then be relatively permanent.  There are also questions about the transient effects during the 'near miss'.  Would tidal forces from the passing rogue planet induce seismic events on the Earth?
This maybe isn't quite the right forum, but have there been any scientific studies along these lines? It also sounds like a good topic for a science-based novel.  Presumably mankind would have years or decades of warning for such an event and would be able to make reasonable predictions about how the environment on Earth will change.  The long-term survival of mankind or life in general in the new environment would be a whole other question.
I do see this similar question and that answer does discuss some important points.
[Edit] But I was hoping that someone might have investigated this scenario in more detail, perhaps with a specific example. I'm wondering if one can do a back-of-the-envelope calculation of how much delta-V the Earth would get from an Earth-size intruder whizzing past at a distance of, say, 1 million km at a speed of 100 km/s. That might allow the range of perturbed orbits and range of insolation and temperatures, etc. to be calculated.


texts: Inconsistent online radius value for Proxima Centauri

texts:
I was looking up the radius of Proxima Centauri and got a funny result.

Google says it's about 100,000 km, while WolframAlpha says its about 200,000 km.  Are the error bars that big, or does someone have some bad numbers?


texts: What percentage of habitable-zone planets are detectable by transit?

texts:
I realize that the probability of detecting a planet by transit depends on the size of the star, the size of the planet's orbit, and the size of the planet; and ranges from ~10% to a small fraction of one percent.
However, the habitable zone of a star is a function of the star's brightness, and thus at least statistically connects the size of the star to the size of a planet's orbit if the planet is assumed to be in the habitable zone.  There is also a known distribution of the relative number of stars of different sizes.
With all that put together, can we form a reasonable estimate of the percentage of habitable-zone planets that can be detected by transit methods? The overall percentage has to be between 10% and about 0.1%, which suggests that if we are able to detect, say, 5 habitable-zone planets within 100 light years, there are probably actually at least 50.


texts: What resolution would earth-moon telescope achieve?

texts:
Event horizon achieved earth-size telescope by using  seperate telescopes around the world to interpolate an image of a black hole at resolution of 60 arcmicroseconds.

What resolution could we get if we built radio telescopes on the moon and used earth-moon orbit to interpolate an image? What could we see with it?

What if we used earth-moon-mars telescope?

Would it make sense to go even bigger?

This is all assuming we would have possibilities to build local telescopes like ones on earth in future.


texts: How to to compute the expected number of collisions between stars when Milkyway and Andromeda merged?

texts: Can some one tell me how you can roughly estimate the number of collisions when Milkyway and Andromeda merged with each other. I know it is somehow related to the mean free path of the star. But couldn't figure out how to do it exactly.


texts: How to use DeepSkyStacker to increase detail, reduces noise, and not lose colour?

texts:
I had my first attempt at shooting the Orion Nebula and am pleased that I saw it for the first time.  Very exciting.  I shot 10 frames and then stacked them using DeepSkyStacker which brought out all the detail but seemed to lose all the colour from the image.  Any ideas what I am doing wrong?

A Raw Single Frame

Stacked TIFF from DeepSkyStacker
I am thinking of combining a single raw frame in PhotoShop as a colour overlay with the TIF output from DeepSkyStacker.  Is that recommended?


texts: What is the effect known as gravitational lensing? How does it work? What objects would be able to cause this effect?


texts: Can solar luminosity & activity be predicted?

texts:
Can a star's luminosity and its activity, solar flares and sunspots, be predicted?

If so, with what accuracy & precision?


texts: Do low-mass red giants last longer than high-mass red giants?

texts:
It turns out that red giant stars are not defined by uniform mass.  Some can be only one-third as massive as our sun, whereas others can be eight times as massive.  So I'm calling the both sides "low-mass" and "high-mass", respectively.
I have been told that red giants last only as long as one billion years, but considering that lower masses equal longer lifespans, I have to ask--is it the high-mass red giants that have the one-G lifespan, or is it the low-mass?


texts: Will galactic filament indefinitely expand while its galaxy clusters indefinitely disperse?

texts:
Exciting discoveries of weak gravitational lensing suggest the existence of galactic filaments made of dark matter that are the size of galactic superclusters. My questions involves the future of the galactic filaments while space indefinitely expands between the galaxy clusters within each galactic filament. Will the filaments indefinitely expand with the indefinite expansion of space or will the filaments divide because of an event horizon? For example, event horizon paradigms suggest that the expansion of space will eventually isolate each galaxy cluster from each other galaxy cluster. Perhaps we do not yet have enough information to calculate this because we know little about dark matter.

I also posted this question at the moderated news group sci.astro.research. A moderator noted: "I think your last statement is definitely true: we don't know enough about dark matter to calculate this."


texts: What is the average luminance of the star background?

texts:
What is the luminance of the star background, i.e. of all the objects outside of the Solar system? E.g. if we measured average luminance of the sky from the far side of the Moon (so that solar and lunar contributions, as well as Earth's atmosphere, didn't count) with the brightest planets being below the horizon, what quantity would we get?
If there haven't been any measurements of luminance, maybe illuminance in the similar conditions has been measured?


texts: Would a large coronal mass ejection affect the earth evenley

texts:
A very severe corolnal mass ejection in the lines of the Carrington event could potentially disrupt power grids and communications,  but would it affect the earth evenly or would the part of the earth facing away at the time be less affected?

This question What are the main differences between solar flares and coronal mass ejections? seems to explain a coronal mass ejection but it does not answer the question about difference


texts: What exactly is wrong with this plaque in Neil deGrasse Tyson's "back yard"? Has it been fixed?

texts:
The Wikipedia subsection Observable Universe; Misconceptions on its size shows this image of a plaque, with the caption:

  An example of the misconception that the radius of the observable universe is 13 billion light-years. This plaque appears at the Rose Center for Earth and Space in New York City.

According to Wikipedia:

  The Rose Center for Earth and Space is a part of the American Museum of Natural History in New York City. The Center's complete name is The Frederick Phineas and Sandra Priest Rose Center for Earth and Space. The main entrance is located on the northern side of the museum on 81st Street near Central Park West in Manhattan's Upper West Side. Completed in 2000, it includes the new Hayden Planetarium, the original of which was opened in 1935 and closed in 1997. Neil deGrasse Tyson is its first and, to date, only director.

That last line is the operative part. Dr. Tyson is a world-renowned stickler for truth and accuracy, and so a problem in is own back yard needs to be investigated.

What exactly is wrong with this plaque photographed in 2011?
What should it have said?
If something is indeed wrong, has it been fixed?

above: Incorrect plaque at the Rose Center for Earth and Space, April 2011

below: Rose Center for Earth and Space Source which literally contains the famous Hayden Planetarium.

Update: I just noticed that even in 2011 the plaque had already been amended (at least) once!


texts: It's been known that the Earth's axial tilt varies from 22.5 to 24.5. Does this result in a wobbling while the value of the tilt varies about these two limits? If so, how does it affect the mechanics of the Earth's movement (its rotation and revolution about the Sun)?


texts: Is the age of the Universe really 13.8 billion years?

texts:
Ok, I know this has been asked by a lot of people, but my reason for asking this question is a bit different. Please read further.
I was watching a video by Fermilab (Start at 6:30, at 8:30 he mentions how we cannot ever see light emitted from objects > 14bn light years away). In it, the presenter Dr. Don Lincoln talks about the speed of light and how some things are faster than that. Expansion of the Universe can be faster than the speed of light, because galaxies 1 megaparsec away appear to be moving at the rate of 68km/s, galaxies 2 megaparsecs away at 136km/s, and so on. So the velocity of the galaxies doubles every megaparsec. If we do the math, the speed of the galaxies moving away surpasses the speed of light at 14 billion light years away.
14 billion is just 200 million give or take more than the current measurement of the age of the Universe.
My question is, at 14 bn light years away the galaxies are moving faster than the speed of light and we can never see anything beyond that ever. Does this mean that even after say 5 billion years (assuming we still exist), if somebody uses the same technique to measure the age of the Universe, they will end up with the same number that is lesser than 14 billion?


texts: a star in the sky thay moves back and forth way up in the sky

texts: did anyone watch the sky in the west at 1:15 am.On 7-13-18. a star moving around in the greenup ky UT WOULD go back and forth


texts: How did Meeus calculate equinox and solstice dates?

texts:
In Astronomical Algorithms (2nd ed, ch. 27, 2009 corrected printing) Jean Meeus gives expressions to calculate the date and time (dynamical time, equivalent to Terrestrial Time) of equinoxes and solstices from the year -1000 to the year +3000. The expressions are accurate to 51 seconds or better for the years 1951-2050. First what Meeus calls the "instant of the 'mean" equinox or solstice" is calculated using a fourth degree polynomial; there are 8 expressions. There are different expressions for each solstice or equinox, and different expressions for the year ranges -1000 to 1000 vs. 1000 to 3000. Then two corrections are applied; the corrections are calculated the same way no mater which time period or equinox or solstice is being corrected. The first step is to calculate:

$$T = \frac{(\text{mean JD of event} - 2451545.0)}{36525}$$

$$W = 35999.373°T - 2.47°$$

$$\Delta \lambda = 1 + 0.334 \cos W + 0.007 \cos 2 W$$

Next, an additional correction is computed involving 24 periodic terms with various periods.

Can anyone explain, in general terms, how Meeus derived these expressions? I'm especially interested in understanding what the "mean" value represents?


texts: Under Earth's gravitational pull, how dense would an object have to be to reach its Schwarzschild Radius?

texts: The Schwarzschild Radius is a theoretical radius, that if the mass of the object was compressed into that certain radius, the escape speed from the surface of the compressed object would equal the speed of light, therefore creating a black hole. But I wanted to know, under Earth's gravitational pull, how dense would an object have to be to reach its Schwarzschild Radius?


texts: How to calculate the temperature of an exoplanet?

texts:
I was given an exoplanet similar in size and distance to host star to our own earth. It's orbiting a star with luminosity six times our sun, the greenhouse coefficient 0.3, bond albedo 0.3.
I would like to calculate the approximate surface temperature (i.e. close enough to know whether it is in habitable range).
Disclaimer: This question was on a past exam and we never got our test back.


texts: Probability of finding life-supporting exoplanets

texts: We've found over a thousand exoplanets by now, but how many of them could support life? What percentage of newly found planets are potentially life-harbouring? Or haven't we found any exoplanets that meet these criteria yet?


texts: What is the highest resolution image of the moon taken from Earth's surface?

texts:
According to this article:

https://www.theguardian.com/science/2018/jul/26/star-spotted-speeding-near-milky-way-black-hole-for-first-time

the Very Large Telescope is "powerful enough to see a tennis ball on the moon from Earth".  I guess that the moon is much to bright and moves too fast for the VLT to take good pictures of it, but it got me wondering: what is the most magnified picture of the moon ever taken from Earth?


texts:
I know the question seems silly, but as far as I've understood, is this the definition of a dwarf planet:

circling around a star, and not being a star itself
having a round shape (otherwise every comet or asteroid could be a (dwarf) planet)
not being able to clear its own orbit (otherwise it's a planet)

If we have a look at Jupiter, then we can easily confirm the two first points, but the third one is an issue: in Jupiter's orbit there are two sets of asteroids, called the Trojans, which are located, together with Jupiter, in some kind of regular triangle, turning around the sun. Following the laws of Kepler, Jupiter and the Trojans have the same speed, so Jupiter can't catch them and although Jupiter's gravity is very strong, it does not stretch to the other side of the sun, which means, following the definition, that Jupiter is a dwarf planet.

I know, Pluto is called a dwarf planet because of the many objects in its orbit, and Pluto's gravity is so small that it can't get rid of those objects. Nevertheless in a scientific you can't use vague wordt like "vicinity", "close", ..., so you can't say Pluto is a dwarf while Jupiter isn't because of the vicinity of the mentioned objects (being "too close").

Do I have a point here or am I missing one? :-)


texts: Software for simulating/calculating a known EMW pulse propagating in ISM, including dispersion, scattering, etc

texts: Could you please let me know, if there is any software/code/tool for simulating/calculating the result of a short EMW pulse (waveform is exactly known) propagating in the ISM for long distance, including effects of especially the dispersion, scattering, etc?


texts: Could vacuum energy dim standard candles?

texts: It is assumed that particles and anti-particles pop out in vacuum (vacuum energy). Could this have an effect on the paths of photons when they interact with these particles? The amount of photons going straight from the source would then gradually diminish. The supernovae would then appear dimmer than without this effect.


texts: What do these coordinates mean: MW - VP101 3° 12' 43.2'' S 5° 12' 39.6'' W?

texts:
I have a jacket with a tag that bears the label:
MW - VP101
3° 12' 43.2'' S
5° 12' 39.6'' W

When I looked it up, I discovered that these are the coordinates of the crater Mosting A. However, I do not know what the letters at the top refer to. Does anybody know what they mean?


texts: What's the difference between GSR and Grf

texts:
I note there are two terms about Galactic rest frame in literatures:
Galactic Standard of Rest (GSR) and Galactic Rest Frame (Grf).

Are they the same frame? If not, what's the difference?


texts: I've downloaded hipparcos catalog from the Strasbourg Universe but whilst there is a lot of information, I can't find the names of the stars that the HipID relates to.  There is the wikipedia page which lists some but not all the stars, for instance Zosma (54872) is missing from the list and don't fancy searching for each and every star page to find out the missing details such as what the HIP's name is, how far away it is, etc.  Is there a downloadable list which lists the HipID, the name, how far away it is, the constellation etc?


texts: Why is [O III] a good density probe in interstellar medium?

texts: According to Draine in his book "Physics of the interstellar and intergalactic medium" (page 210/211) and Caltech [O III] line ratio's (amongst others) are a good density probe, but I cannot really understand why that is the case. Can someone explain me how this works? It doesn't have to be numerical or with detailed formulas, just the idea what is going on.


texts:
Planets sweeps out equal areas in equal times.

Is the area being calculated here the area of a triangle? You draw a straight line from the center of the sun to the earth at point A. The Earth moves to Point B and you have another straight line from point A to point B and the finally another straight line from point B to the Sun? Even though the Earth makes an arc, I guess we make it a straight line.

I guess my question is whether I have understood the second law correctly? That the area of a triangle was being calculated in an elliptical orbit, no matter how elliptical the orbit is.


texts: How much the moon movement can influence an equatorial mount setup?

texts: If I use an equatorial mount for my telescope to view the moon, is there a way to take in count the moon movement around the earth, or the movement is too small compared to earth rotation?


texts: How could we tell if the Universe is infinite?

texts:
I've heard from a number of people that the Universe is infinite, and from my perspective, I can't see how this can actually be known, especially given that the Universe started out a finite size and grows at a finite rate.

  Regarding the possible similarity of my question: I want to know how
  it could be and how we would know, rather than if it is. This is
  significantly different.


texts: Gravity of other objects in black holes?

texts: If something falls into a black hole, but has not yet hit the singularity in the center, can we (outside of the black hole) feel its gravity? On the one hand, I've learned that there's no distance limit to gravity and that everything in the universe feels the gravity of everything else. On the other hand, we would be able to measure the gravitational field of the thing and thus figure out where in the black hole it is, which contradicts the idea that no information can escape a black hole.


texts: Position of specific stars in the sky as a function of time

texts:
I'm a beginner in astronomy and I'm trying to figure out how to model the positions of stars in the night sky mathematically (ie a function which spits out azimuth and altitude as a function of time). I was wondering if anyone knew of any such function, I understand it would vary with your position on earth.

Furthermore, does anyone know anything about the mathematics of star movements, I'm trying to learn all I can.

Thanks!


texts:
as a follow-up to my previous question I found out that the Voyager Golden record uses a star map of pulsars to precisely show where our solar system is...

Is it possible/feasible to base a navigation system on pulsars in order to replace GPS?


texts: Observatories with public access in Europe

texts:
This is a follow-up to Observatories that allow public access with a smaller (geographical) scope.
I am interested in getting to know observatories in central Europe (e.g. France, Germany, Poland, Switzerland, Austria) where you could could go with a class of school children or university students.
Maybe you could add more entries to my list, please?

The Effelsberg radio telescope has a visitor programme.
The Heidelberg observatory has some outreach programme, but is close to a city with its lights.
Similar problems with light pollution has the Paris Observatory.

I tried to find some European website with such a list, but I was not successful yet.


texts: I was reading about how powerful supernova were and found out there are even bigger supernovae also called hyper nova.  A large explosion was discovered in 2016 I believe (or was it 2017).   I would like to know on a human scale how much power that is.  Suppose an inventor produced an engine technology that has the output of the largest superluminous super nova to project a space shuttle.  How fast would the space ship be projected forward?  That is the output pushes air to project the space ship forward.  What speed would it reach.  Part of me wants to say faster than light.  I imagine the ship will travel so fast it would disintegrate since matter cannot exceed the speed of light.


texts: Public Data Set on Atmospheric Absorbtion / Extinction

texts:
Is there a publicly available data set for mean atmospheric absorption / extinction? I would like to be able to process and plot a graph similar to this image from NASA on wiki commons.

The HITRAN database appears to offer individual lines and might possibly be used to compute mean absorption at standard atmosphere. However, the process is unclear and the data search appears to be broken.

Spectral Calculator by GATS also appears to have done the calculations for various configurations pulling from the HITRAN database and using standard atmosphere, but access to transmittance and absorption plots is limited to subscribers paying $50 per month.

A lot of individuals seem to be generating or copying these plots, but very few citations are given. Furthermore, indications are that there may be a fair amount of variability depending on conditions so a plot based on standard or mean conditions looking upward or downward through the atmosphere would be helpful.


texts: Convolve a SED with a filter. Is convoluting the mathematical operation?

texts:
I know that in order to get the Flux of a star (or something else) in a particular filter from its SED (luminosity per unit wavelength), I need to convolve the spectrum (SED) with the filter response. Most of the formulas I see to do this are
$$F_{b}=\dfrac{\int f(\lambda) T_{b}(\lambda)d\lambda}{\int T_{b}(\lambda)d\lambda}\,,$$
where $f(\lambda)$ is the SED, and $T_b$ is the filter response in band $b$.

This formula seems very different from a mathematical convolution that I would write as
$$f*g(\lambda)=\int_{-\infty}^{\infty} f(x) g(\lambda-x)dx\,.$$

Are these two convolutions the same thing? Or is the "astronomy convolution" a different thing (e.g. SED Fitter python package)?


texts: Question about extreme space distortion and creation of a new dimension

texts:
In all the illustrations regarding space distortion, I find an extra dimension that depicts space distortion. Is there any mathematical equation that proves the creation of an extra dimension ?

Thanks.


texts: What happens to a white dwarf past the Chandrasekhar limit?

texts:
This is a multiple choice question I had trouble with on an exam.

Will a white dwarf that has had too much mass piled on top of it

a) undergo a thermonuclear flash and explode in a type IA supernova

b) collapse to form a black hole

c) collapse to form a neutron star in a core collapse (type II) supernova


texts:
Let suppose you are at +3 degrees latitude (3 degrees north of Equator ... for example at Cali in Colombia). At what periods of the year will the sun be at your vertical (at your zenith) at noon?

I know that at Sun is at equator zenith on 21st March and 21st September (spring and fall equinox). So at +3 degree north of equator will it be before or after 21st march? And before or after 21st September?


texts:
Using the SIMBAD database for Alnitak, Saiph, and Sirius -- i.e.:

Alnitak: FK5 coord. (J2000): RA = 05 40 45.527 DEC = -01 56 33.26;
Saiph; FK5 coord. (J2000): RA = 05 47 45.389 DEC = -09 40 10.58;
Sirius; FK5 coord. (J2000): RA = 06 45 08.917 DEC = -16 42 58.02;

What is the trigonometric relationship in degrees -- length of sides and inclusive angles to four decimal places -- between these three stars when they are used to form a triangular aterism?


texts: Sun's and planets' inclination to the Invariable plane

texts:
What are the inclinations of all major Solar system planets (Mercury to Pluto) to the invariable plane? Looking for accurate data calculated on them.
Also, What is the inclination of the Sun to the invariable plane? Since Sun revolves around the barycenter.
If a planet has an inclination to the invariable plane, that means at any point in time the degree is different depending on the planet's position. where can I get this information of planets' inclination degree at any date? Calculated by NASA JPL Horizon?


texts: Could space time curve from the vantage point of earth and out into the universe, and would d = 1 / P in that case give false estimates?

texts:
The seventeenth century saw a revolution in astronomy. The invention of the telescope and the acknowledgement of the heliocentric system triggered a race amongst astronomers to measure the parallax of stars - the annual displacement of stellar positions due to Earth's motion around the Sun. In the late 1830s these measurements enabled astronomers to determine the distances to a handful of stars for the first time. From the 1850s onwards, the application of photography to astronomical observations transformed the practice of charting the sky, allowing the compilation of larger and larger catalogues of stellar positions and distances.

That robust marvel of trigonometry applied to observations of other stars, lets me look up into the sky for 6 months, measure the apparent motion, then divide 1 by that, and voila, the distance to the star.

For example, the distance to Alpha Centauri, https://www.wolframalpha.com/input/?i=1+%2F+.77

These distances are used in all textbooks, all databases, all conversations, and does not correct for any space-time curvature whatsoever.

To draw a line on the sky, and use trigonometry, seems almost a bit too simple. Anyone have any thoughts on if space-time might curve in weird ways sort of like how a fish eye lens on Instagram distorts an image?


texts: In a story I'm working on, a huge, 20 by 14 kilometer, Ni-Fe asteroid attains a 1760 km. orbit around earth (why/how? Long story). I figure it has an H magnitude of ~12. Would this body be visible naked-eye from the surface during the day?


texts: What if the two Black Holes spiraling around each other are evaporating via their Hawking radiation?

texts:
A non-technical explanation
In a Gravitational Wave event, the point is that in this event when Black Holes are spiraling around each other, they will cause the very fabric of Space-time to ripple and this event is an energetic event and those ripples travel at the speed of light and  we can describe mathematically that how this could happen and how these Waves of Gravity travel. Now, my question stops here and my question is that as we all know Stephen Hawking came up with a Beautiful explanation that Black Holes aren't so much Black as we thought of, in time, they can evaporate and that would bear the name, ''Hawking Radiation''. Now, this implies to Black Holes, and still we haven't detected Hawking Radiation yet and Hawking didn't had a Quantum Theory of Gravity.
So, if we consider for example, that Black Holes can evaporate, so they must evaporate when they are also spiraling and what will happen in this case? If the spiraling Black Holes can evaporate via Hawking Radiation, how will we detect it and what will the mathematical equations describing this Event be?


texts:
I want to add realistic noise to a simulated image but I am a little confused about the process. I want to have some Gaussian random noise representing the readout noise and to also add Poisson noise correlated with the signal in the image.

I understand how to add the Gaussian random noise; I draw samples from a Gaussian with fixed width and add the samples onto the pixel values.

I am confused about the Poisson noise though. Is this noise only correlated to the noiseless signal?

i.e I should draw samples from the Poisson distribution with $k = \mathrm{pixel  value}$ (before adding the random noise) and add it to the noiseless image.


texts: How is a non-rotating black hole created

texts:
How are non-rotating black holes formed?

I guess that non-rotating black holes are formed from non-rotating stars but I couldn't find any proof that such a star exists on the internet. If this is true can you also put up an example of such a star?

Does the matter absorption of a non-rotating black hole differ from a rotating black hole?


texts: Isn't it absurdly unlikely that our Moon would constantly be "facing" us?

texts:
I never thought about this until recently, but our Moon is constantly rotating in such a way that it happens to perfectly be "looking at us" at all times. That sounds incredibly unlikely to me.
Couldn't we just as well have had a moon which constantly shifts patterns by rotating in a different manner, rather than us always seeing the same craters on the "moon's front side"?
I can very much understand that this mislead people "in olden times" to assume that this universe is constructed in a very different way from what it actually is. If the moon had been "shifting in pattern" from day to day, or even hour to hour, or even minute to minute, it would be much easier to conclude that it's a spinning orb far away, orbiting our orb. Or at least that's what it feels like to me.
The fact that the moon is always "looking at" us seems highly unlikely. It's rotating around us, but also rotating itself in exactly such a way that it appears to be "fixed" from our surface as we look at it. It's very strange to me.
How did we end up with such a moon? Wouldn't the far, far more likely case be a "spinning" moon rather than "fixed" one? Maybe the moon would orbit us but not rotate at all? (I'm unsure what that would look like from here.)
Or is there something I'm missing here?


texts:
The astronomical zodiac contains a bunch of constellations along the ecliptic.

Some sources say there are 13 constellations in the astronomical zodiac. Other sources claim there are 12.

According to NASA (source):

  If we count all the traditional constellations, there are 13 in the
  zodiac, not 12. So here are the dates (give or take one day each year)
  when the Sun is between Earth and each of these 13 constellations.)

There seems to be some confusion out there between zodiac constellations (in astronomy) and zodiac signs (in astrology). From the research I've done so far (including the quote above), it seems as though one of them (Ophiuchus) is a "recent addition", possibly due to the Earth's precession since ancient times (source).

What (officially?) are the constellations of the astronomical zodiac?
Why do some sources list 12 and others list 13?


texts: If you're near a black hole and your time is slowed down, would a supernova be observable to both you and someone outside of the blackhole's pull?

texts: Let's say that Person A is on a planet orbiting a black hole (like the one from Interstellar) and time is slowed for Person A. Person B is back home on Earth. Now let's say a supernova happens and it's possible for both parties to see it happen at the same time (ignoring the time it would take for the light to get there). Would Person A see the supernova at the same time as Person B? And if so, if Person A is in 1,000 B.C. and Person B is in 2,000 A.D, would the supernova then happen at two different times at the same time?


texts: Why are O III lines so prominent in the spectra of emission nebulae when the amount of oxygen relative to hydrogen is a million times smaller?

texts: Looking at spectra of emission nebulae like the Lagoon Nebula, the $[\text{O III}]$ lines are prominent in intensity. However, the abundance of oxygen is minuscule compared to hydrogen. How then are the $[\text{O III}]$ spectral lines of such high intensity?


texts: Why does the Tycho-2 catalog not include Hipparcos stars?

texts:
Both use the same data. But at least, 90k stars are lost in Tycho-2.
Why?


texts: Scientific evidence against CMB originating from “Oort Soup”?

texts:
In this article (and references therein) the author claims that the Cosmic Background Radiation can be explained as black-body radiation originating from the cold bodies filling the interstellar space (which the author refers to as “Oort soup”).

As far as I know, the mainstream point of view is that CMB is an echo of the Big Bang which dates back to the electroweak symmetry breaking,and has cooled down since then due to the expansion of Universe.

This is the first time I learned about the alternative “Oort soup” hypothesis, which, according to the Author, also favors the Dark Matter model made of cosmic dust. I don’t have enough evidence to judge for myself whether it is pseudoscience or a valid alternative explanation of the CMB.

I would like to know what the position of the scientific community is — is the hypothesis considered pseudoscientific, or a valid (though maybe unlikely) alternative? What scientific evidence against the author’s hypothesis do we have?


texts: How far apart is the dust in the Sombrero Galaxy's dust lane?

texts:
In his answer to this question, TildalWave made this remark:

  I think that first, we have to properly appreciate the size of the Sombrero Galaxy. It is roughly 50,000 light years (15 kilo parsecs) in diameter. That might be only half of the diameter of our own Milky Way galaxy, but still makes each and every pixel on the photograph you're attaching in your question stretch more than 100 light years in distance.

Here's the photograph:

Since it almost feels like I can see individual 'pieces' of dust in the lane, it would follow that the particles must be very far apart. Just how far apart are they? Are they grouped in clumps, or relatively evenly space?


texts: What is the effect of extinction in the accretion disk for black hole mass determination?

texts: I've created a basic model of the accretion disk (AD) by summing up blackbodies following the temperature profile of the AD according to Shakura & Sunyaev (1973) (extensively used in the literature to model the AD, nothing new). As you can see in the figure (left the spectrum, and right the SED, both rest-frame), I compare 2 objects at similar redshift, one object more massive, luminous, and accreting more (parameters of both objects inside figure; left). The object with a larger black hole mass (bhm) (Blue line) has the peak luminosity (right panel) at lower frequencies (longer wavelengths) and has a larger accretion rate, therefore it is more luminous, etc. Now, if one should correct by extinction due to dust in the "vicinity" of the accretion disk (AD), the shorter wavelengths are more affected by such extinction and therefore the corrected AD emission will be stronger at shorter wavelengths (higher frequencies). After the extinction correction, the object will appear to have more luminosity, accretion rate but a smaller black hole mass. For example, if the blue object is corrected by extinction, then the blue line SED will shift to the right. Question: Do you think this reasoning is correct? it seems a bit counterintuitive or? especially since one would expect, more accretion, more mass after correcting by extinction.


texts: Can a black dwarf be suitable for manned exploration, once it cools down? And potentially used for space mining?


texts: Solar series 142 and 147 started same year - series 147 and 152 will be ending same year. Why? Coincidence?

texts:
This question was left over from the last question I had, so I am asking it separately here:

I have been looking into two solar eclipses (Saros series 147 and 152) that will both be occurring in 2021. Each of these eclipses will be happening near the opposite poles of the earth.  Both are part of young saros series. Saros 152 is comprised of 70 eclipses, while saros 147 contains a total of 80 eclipses. These series are 10 eclipses difference in length and began 180 years apart. So, I happened to check out their ending dates and found that both series are projected to end during the exact same year - 177 day apart – together in the year 3049. I thought that both of these series ending together one semester apart in the very same year was a pretty amazing coincidence.

So, checking further – it seems new saros series start from as few as 7 years apart to as many as 100 years apart (this is extremely variable spacing, but it averages to about 31 years apart over the usual 1260+ year active series lifespan). I wanted to know why series 147 and 152 would both be ENDING at the same time.  I went back to the NASA website, and checked the 5000 year listing of all solar saros series numbering 0 through 180. I only found one other such instance of two solar saros series ENDING in the same year – series 49 and 54 both ENDED together in 32 CE – so it seems like a pretty rare event.

But then, I checked to see if there were any occasions of two saros series BEGINNING together in the same year. Going back to the NASA website again with this question, I checked the 5000 year listing of all solar saros series numbering 0 through 180. I only found one single example of two saros series both BEGINNING in the same year. This time series 142 and 147 both BEGAN together in the year 1624 CE.

Not only is solar saros 147 involved in BOTH of these "same year" cases, but all three series eclipses will be presenting themselves during a single upcoming semester series in 2021 – solar series 142 (Dec 14, 2020), 147 (June 10, 2021),
and 152 (Dec 4, 2021).

  Can anyone explain to me the actual mechanics behind what causes saros series to begin and end? I am familiar with Saros/Inex
  Panorama – but unfortunately they do not answer this question, and I
  can’t even read them online anyway.

  Does anyone know why solar saros 147 may have STARTED in the same year as saros 142 or why saros 147 will be ENDING together in the same
  year as saros 152? Are these two occasions both very rare
  coincidences, while at the same time, both involve the same series 147?


texts: Is liquid water on Mars such a big leap compared with ice?

texts:
I thought we have found bacteria or other kinds of life on Mars.

Now it is liquid water.  Is there such a big difference between liquid water and iced water?


texts: Which galaxy is receding from the Milky Way the fastest? What is known of the mechanism behind its recession?

texts:
Galaxies are always in motion relative to the Milky Way. My question is, which galaxy is receding the fastest from our viewpoint?

What is the theorised mechanism that causes this?


texts: The battle over Gliese 581 and Gliese 667C?

texts: In 2014, Robertson et al. made a case that stellar activity is masquerading as planets (here and here) for these well-known systems. In both cases, they claim that the only real planets discovered so far are planets "b" and "c". In 2015, Anglada-Escude et al. questioned the methods of Robertson et al. (here). Also in 2015, Brewer et al. suggested that there is evidence for multiple planets at Gliese 581 here (note, I only have access to the abstract - fulltext is here). Is there a direction that a majority of the professional community is leaning?


texts: What orbital period would produce one New Moon (and one Full Moon) each year? What other effects would this produce?

texts:
I am interested to know whether it's possible for the moon to orbit the earth at such a rate that we would see only one New Moon and one Full Moon a year. If so, what other effects would we experience?
I at first assumed this would be a one-year period, and technically I think that would produce one New Moon, but that single New Moon would last all year (i.e., you would never see the moon). So I'm interested to know if there is an orbital period that would give us one New Moon and one Full Moon, as seen from our earth, each year.
As I hold my hands up in front of my face and experimentally rotate them around each other, I want to say a six-month period would produce this effect, but I'm not sure that's correct, so I'd appreciate a word from anyone who actually knows what they're talking about. Thanks!
(Apologies if this has been asked before; I wasn't able to find it.)


texts: How come the northern and southern lights are the same?

texts: Not an expert, hence the question. To my knowledge the magnetic field of the earth travels south to north. Wouldn't there be a bias on whether the charged particles causing the auroras are negatively or positively charged? If each pole attracts the opposite, how come they're the same?


texts: Gas is abundance in the universe, can a massive asteroid draws in these gas forming a thin atmosphere?


texts: How would the sky look if Earth orbited a red giant at a safe distance?

texts: Let's say that instead of the sun, we have a red giant, but are orbiting it at a safe distance, within the goldilocks zone. Would the sky actually look more red? Or would it be closer to white/transparent due to a shortage of blue light for Rayleigh scattering?


texts: Calculate the absolute magnitude for a multi-star system

texts:
We know that the absolute magnitude of a single star can be calculated with the formulae:
$$M_{\rm bol} = 4.75 -2.5 \log_{10} \left(\frac{L_*}{L_{\odot}}\right)\ ,$$
$$M = -2.5  \log_{10}(L_* / L_0),$$
where $L_*$ is the luminosity of the given star, and $L_0$ being the luminosity of a magnitude 0 star at a distance of 10 pc ($79L_\odot)$.
However, this only works for a single star, not multiple star systems. Is the formula for the absolute magnitude of a multiple star system defined as $L_*=L_1+L_2+...+L_n$ (the sum of all luminosities in the system), where $L_n$ is the luminosity of a star in the system, or is it something else?


texts:
I am writing a blog post and while I am interested in astronomy I havent done any physics like this since high school. My question is: what would the mass and density of Sirius A be if the mass of Sirius B is roughly the same as the Earth? If Sirius B is actually only as heavy as the Earth then Sirius A would need to be far less dense. How dense would it need to be to be the same size it currently is and what would its mass be?
The orbit of Sirius A and Sirius B has been observed. But the true mass and density of Sirius A and Sirius B cannot be known with certainty like with the orbit. So, it is possible that Sirius B actually has the mass and density roughly equal to the Earth. The light we see when we look at Sirius B is some kind of alien technology they are using to block out cosmic radiation.
If this fictional scenario were the case then what would the mass and density of Sirius A need to be in order for the orbits to be the same given that Sirius B has the mass and density roughly equal to the Earth?
Additionally, how dense would Sirius A be compared to Betelgeuse in this scenario?

The orbital motion reveals that Sirius A, the brighter star, has 2.02
± 0.03 solar masses and Sirius B, the white dwarf, has 1.00 ± 0.02
solar masses.
Betelgeuse has a radius 1,100 times that of the Sun but its mass is
only about 8 – 20 times the Sun. This means the density of Betelgeuse
is much, much lower than the Sun. The average density of Betelgeuse is
about a million times less dense than Earth’s atmosphere at sea level.
That’s about the same as a vacuum found in an insulating Thermos
bottle.


texts: How do GHA of vernal equinox, GHA of astronomical object and RA relate?

texts:
I have zero clue in astronomy and I need astronomical data to write a program. What I learned so far:

celestial coordinates are usually measured relatively to vernal equinox aka meridian of First point of Aries (which is not located in Aries anymore)
the GHA of first point of Aries changes constantly

I was searching for vernal equinox GHA data and it seems to me that this personal, generated Almanac version lists it as "Aries" (it was misleading me).

I expected that
( GHA(object) - GHA(v. equinox) ) mod 24h = RA (object)
as per this article. However I have found a program which calculates declination and right ascension and I have found out that the relation is sort of inverse. For example:

https://sv-inua.net/wp-content/uploads/2016/12/almanac2020.pdf

And the program output:

               The Moon

  JD 2458849.50,  2019 December 31 Tuesday 23h 58m 49.174s  UT 2020
  January 1 Wednesday  0h 00m 00.000s  TDT nutation dRA -1.043s dDec
  -6.12" Geometric lon -13.866 deg, lat -4.894 deg, rad 2.6996e-003 au   Apparent geocentric longitude 346.129 deg   latitude -4.894 deg
  Distance 63.319 Earth-radii Horizontal parallax    0d 54' 17.67"
  Semidiameter    0d 14' 47.60" Elongation from sun 66.20 deg,
  Illuminated fraction 0.30 Phase 2.0 days before First Quarter
      Apparent:  R.A. 23h 16m 38.283s  Declination -  9d 58' 41.62"
  Local apparent sidereal time   1h 54m 46.005s diurnal aberration dRA
  0.012s dDec -0.03" diurnal parallax dRA -104.977s dDec -2485.74"      atmospheric refraction 0.033 deg  dRA 4.296s dDec 102.06" Topocentric:
  Altitude 25.678 deg, Azimuth 224.447 deg Topocentric: R.A. 23h 14m
  57.615s   Dec. - 10d 38' 25.32" local meridian transit 2019 December 31 Tuesday 21h 16m 02.396s  UT rises 2019 December 31 Tuesday 15h 49m
  26.475s  UT sets 2020 January 1 Wednesday  2h 50m 11.075s  UT Visible hours 11.0124

So:
110 deg 56,9 sec - 100 deg 7,1 sec = 10 deg 49,8 sec
which is inverse of R.A. which program lists.

Do I have a misconception?


texts: Maritime telescopes: Stabilisation requirements for optical vs. radio telescopes?

texts:
SOFIA stands for Stratospheric Observatory for Infrared Astronomy. She says:

My telescope stays stable with a spherical bearing, shock absorbers, and gyroscopes.

I suppose a similar system would work for an optical telescope on a maritime vessel as well. But what about a radio-telescope on a ship with a dish of around 10m? What are arguments (ideally mathematical ones) against a similar construction like for SOFIA?

References

Tom Nardi A Miniature Radio Telescope In Every Backyard. hackaday.com (2019)
Gregory Redfern: Cruise Ship Astronomy and Astrophotography - The go-to astronomy resource for cruise travelers


texts: Is there an official list of objects in the sky?

texts:
I would like to know how many known quasars there are in the Universe as well as x-ray binary black holes (not Neutron stars) but I don't seem to be able to.

I also want to know how many black holes have been found via gravitational wave detections but I think the answer to this question is 3.

Do you guys know any credible sources that list the objects in the sky via category and gives detailed info of how we found them (x-ray binary or gravitational waves or quasars).


texts: Is it POSSIBLE that we are a binary system? I have been doing research into this topic and it seems we may infact be a binary system. If we are, what effects would a massive body comming into our system be? And are these effects happening now?


texts: When astronomers "look into the past" are they accounting for the expansion of space?

texts:
Every time astronomers look "13 billion" years into the past, not only is there more space than there normally would be at that instant which increases from observation to observation, but there was also expanding space for eons prior to that which must offset photons over those billions of years.

I haven't seen astronomers ever actually state they've reconciled that difference whenever they talk about their observations, so

1: Do they actually?

2: How do they?

3: How does that change the reality of their public statements?


texts: How tightly clustered are the CHIME-detected FRB repeats?

texts:
In the past few days, journalists have been playing the usual "X could be aliens" game. This time, X is repeating FRBs from a galaxy 1.5 billion light years away. (Or is it 1.5 billion years ago? The proper/conformal time distinction isn't clear in pop sci.) I couldn't find the galaxy's name anywhere, but then I suppose a galaxy that distant might not have been named, even if it's now of some interest. Still, the claim of "repeated" bursts (regardless of their cause) made me wonder: what is our tightest empirical upper bound on how far apart the detected bursts' sources are?

I'm prepared to believe we can see 1.5 billion light years away, clearly enough to pin two events to the same 100,000-light-year wide galaxy, with no others within 2 million light years of it (these are plausible example numbers based on comparing the Milky way to Andromeda). They're small fractions of 1.5 billion light years, but not so small we couldn't resolve an image that clearly. On the other hand, I sincerely doubt we can prove any two bursts that distant are from the same star. I presume what's notable about repeat FRBs is they're so close together in time we expect the source to be common, but I'm curious as to how tightly observations constrain that.


texts: Mountains on the moon during solar eclipse?

texts: I ask myself the reason of why the sun in not uniform on the edge of the moon at this moment of the eclipse (cf. picture) is not unifom is because of the mountains of the moon ? Or can it due to erruptions of sun ? If not is there another reason to explain that ?


texts:
This might sound like a strange question, but something got me thinking about it recently.

The opacity of plasma in stellar interiors can get quite high, making for shorter free-paths for photons. In these conditions I guess that the light you could theoretically gather, supposing you have a pair of indestructuble eyes submerged in the solar interior, would be the one emitted by the plasma in your immediate surroundings, right? So if the opacity is high enough I can imagine places inside a star like the Sun where there is the same ambient illumination as a typical moonless night here on Earth.

My questions are:

Is this line of reasoning correct?
Are these conditions actually possible inside a star?
Where exactly inside a star are these conditions possible?


texts: Which astronomer set his beard on fire because he left the cap off his telescopes finder?

texts:
There is a famous story of an experienced astronomer setting his beard on fire because he left the cap off his telescopes finder. I know it's said to be true of Galileo, but I thing it's relatively recent - i.e. 20th century.
Does anyone know his name? Or can someone cite a source?


texts: Benefits to adding a 32mm Pössl to my Celestron AstroMaster 130EQ's eyepieces?

texts:
I am getting a Celestron AstroMaster 130EQ soon. I have heard that its eyepieces aren't the best, so I am considering a 32mm Pössl.
For such a choice, what would be the arguments for and against? How would my viewing experience improve, and for what objects would this be most and least obvious?


texts: Looking at the Expanding Universe through the lens of relativity

texts:
The basis and most observable metric for how the universe is understood to be expanding at an accelerating rate is the red shift in observable light.  I am assuming it has been thought about or maybe it is just obviously wrong to people with more knowledge, but why can we not say the universe is technically always collapsing on itself under gravity's pull when considering relativity?

We know that space and time are affected by gravity so if we think in relative terms if everything is accelerating at an accelerating rate towards everything else this could explain the red shift (appearance of moving away). Things behind me would be accelerating slower towards the singularity things in front of us would be accelerating faster. Therefore relative to us it would actually look like it is all expanding at an accelerating rate, explaining the red shift.

In this very simplistic thinking, this would work for a universe that expands and contracts or is in a never ending state of contraction, which relative to us could go on infinitely since time and space is all intertwined with gravity.


texts: What effect do aircraft have on night-time visibility?

texts: I have something of an interest in astronomy. I also have a 5" reflector telescope, plus of course binoculars. With the recent coronavirus emergency, a large number of commercial aircraft were grounded. It seemed to me that the skies were much clearer as a result. Now the planes are flying again, and the opposite seems to be true. Is this just my imagination, or pot luck? Do commercial aircraft have an effect on the clarity of the night-time sky?


texts:
Simple question here. I am working on something that needs to compute an orbital path using Keplerian Elements. When doing some research I came across this JPL page: Click Here. Within that link is a PDF titled 'Keplerian Elements for Approximate Positions of the Major Planets'.
From what I can tell, it looks as though this PDF is an excerpt from a larger document. I'm making this assumption based off of the equation numbering. They start at 8-30. From my experience, this is usually due to the fact that there were more equations/sections preceding these equations in the overall doc.
I would love to explore this larger document in order to learn more and find some answers to questions that have developed after reading through the doc. Does anyone know what this document is taken from?
Thanks!
Full Answer
Just for those who are looking for a complete answer to this question, I wanted to combine the two answers below into one complete answer (without taking credit and making my own answer).
As JamesK mentions, this excerpt is actually pulled from the book, Explanatory Supplement to the Astronomical Almanac. I now own this book and it is chock full of useful information, including the excerpt I was looking for. It also dives into a deeper explanation of everything in the excerpt I posted. If you don't want to buy the book, Huy Pham provided a link to the full chapter that includes the excerpt I linked.


texts: How often does Earth cross the galaxy regions with higher supernovae activity?

texts:
According to Summa Technologiae, a book by a Polish author Stanisław Lem that based his science fiction novels on scientific research of the era, the Earth crossed in the moment of forming of life the arms of the Galaxy, with high supernovae activity, which triggered life creation. Afterwards, it moved to regions with low supernovae activity, which enabled the preservation of existing life.

I'd like to test the validity of this claim against current research. How often does the Earth cross regions with higher concentrations of stars (and therefore, much greater chance of gamma burst wipe)? Additionally, how many times the probability of nearby supernova explosion is higher in that regions?


texts: Is a black hole made from a anti-matter star the same as a ordinary black hole?

texts: Would a black hole from a star made of anti-matter be the same as a blackhole made of ordinary matter?.


texts: I've heard from renowned astrophysicists that we don't yet know whether or not the Universe is infinite. How is that possible regarding the big bang theory is accepted (as they all do)? Are they referring to the existence of other Universes when they say it could be infinite, or what?


texts: Is the water underneath Europa's ice cap potable?

texts:
I read this question on Worldbuilding.SE, and figured that the astronomy site would have answers too, particularly for the specific example of Europa. The idea is that Earth's oceans are salty because rain falls on continents, and while the rain makes its way to the sea it absorbs minerals and salts from the land. That piles up in the oceans, and that's why you can drink river water but not sea water.
Europa has no continents; as far as we know it's an ice cap of a couple tens of km, then roughly 100 km of liquid water, and only then something rocky that might contain salts.
Does that mean that the mentioned liquid water is likely to be pure? Or at least pure compared to the Atlantic Ocean? Or do we not know?


texts: What is the limiting abundances of elements at the end of the stelliferous era?

texts:
Is there any reputable published source on expected elemental abundances at the end of the era of stellar fusion? I am here interested in the contents of galaxies; much of intergalactic gas will be lost and remain primordial.

Adams & Laughlin mention estimates of Timms that the final chemical composition will be $X\sim 0.2, Y \sim 0.6, Z \sim 0.2$ but does not analyse the composition in much detail beyond the chemical evolution of white dwarfs (which mostly happens in the later degenerate era). Fukugita and Peebles also make use of a very approximate estimate.

It seems entirely doable to run an IMF model, add some intergalactic gas infall assumpptions, add some recycling assumptions for different mass classes, generate a composition and iterate until a limiting value. But it also seems to be a lot of work that I strongly suspect somebody has already done somewhere far better than I could do.

Another, very crude, approach might be to argue that since we know the cosmic element abundances today after 13.6 billion years of stellar activity we can rescale them to a limiting value: $A(t)=A(\infty)(1-e^{-t/\tau})$ where $\tau$ is the timeconstant of stellar elemental conversion. That would give the desired $A(\infty)=A(t_\mathrm{now})/(1-e^{-t_\mathrm{now}/\tau})$ (at least for metals; hydrogen and helium would be depleted). This assumes that the rate of conversion does not change (highly doubtful, since it will be more red dwarf conversion of hydrogen to just helium in the future than in the past where many more heavy stars formed due to the peak of SFR). If we use the estimate that $Z$ will increase by a factor of 10 from the current $Z\approx 0.02$ we get $\tau=1.3097\cdot 10^{11}$ years which seems reasonable, and of course just $A(\infty)=10A(t_\mathrm{now})$. That would for example make 10% of the mass oxygen and 4.6% carbon. But it would be underestimating the r-elements produced in neutron star collisions (since these were more rare in the past) and cosmic ray spallation elements.


texts: Names of specific galaxies in Hubble's XDF

texts:
I'm working on a little side project that traces and identifies galaxies in Hubble's XDF using OpenCV.

This is my current progress with tracing the more prominent galaxies:

I was wondering if there was some kind of database for the galaxies that appear in the XDF. Like their scientific names, coordinates, distances, and etc.

Here's a link to the image I am using for the project: https://www.nasa.gov/mission_pages/hubble/science/xdf.html


texts: What (actually) is Jupiter doing to this year's Perseids meteor shower?

texts:
After reading the Astronomy Magazine article Perseid meteor shower set for its best show in nearly 20 years and NASA's Look Up! Perseid Meteor Shower Peaks Aug. 11-12, I understand that Jupiter's gravity is affecting this year's possible peak rate of Perseid's meteors.

I think it is - in simple terms - deflecting some of them out of their general orbit, a bit more towards earth, so that we intercept more than usual. But I am having difficulty visualizing this. Is this deflection in the plane of the ecliptic, or out of plane? At our closest approach, how far away are we from the orbit of this dust?

A good diagram would really help!  I found this at space.com credited to Jeremie Vaubaillon, but it's not helping me with the 'big picture'.

Also found this here and credited to NASA/JPL:


texts: Integrating radial velocity with respect to time

texts:
I'm a highschool student who is writing a research paper about plotting Period-Luminosity graph of the Cepheid variables by deriving distance through independent method such as trigonometric parallax and Baade-Wesselink method:
$$∆R = R(t) - R(t_0) = -p \int_{t_0}^t v(t)dt$$

While trying to understand and use the Baade-Wesselink method, I faced some difficulties in terms of calculating linear radius variation. According to some papers, I need to integrate radial velocity with respect to time to get the linear radius variation from $t_0$ to $t$, where $t = t_0$ $+$ its period.

I got the linear radial velocity from the SIMBAD database. For example, for the V* AQ Pup (one of classical Cepheids), its radial velocity is 56.9km/s. Then how do I integrate this value from $t_0$ to $t$? Does this mean [56.9t]^t_t0 and after all $56.9t_1 - 56.9t_0$?

And also, may I ask how can I get the value of $t_0$ and $t$? Does this mean "proper motion" in here?


texts: Rewriting the equation for the virial mass of a cluster

texts:
I have a question that I don't know how to solve, any help is appreciated.

Here it is:

Rewrite the equation for the virial mass of a cluster so that if velocities are entered in km/sec and dimensions in Mpc, the resulting mass is in solar mass

Well the equation is: $M=\frac{5(v_r)^2R}{G}$

I think I have to use dimensional analysis but I really don't know how to get there

$$[M]=\mathrm{\frac{(\frac{km}{s})^2 km}{\frac{m^3}{kg \cdot s^2}}}$$

with one $\mathrm{mpc}$ being $3.09 \times 10^{19} \ \mathrm{km}$

Thanks in advance :)


texts: Does the axis of a galaxy as a whole "wobble" the same way that the Earth does?  If so do we have any idea how much or how fast the Milky Way is doing so?


texts: Why does Stellarium tell such imprecise distance for Betelgeuse?

texts:
The newest version of Stellarium, as well as the former ones, tell that Betelgeuse would be 497.95 ly plus/minus 56 ly away. Celestia also lists Betelgeuse ~500 ly away, but Celestia is comparably old. Isn't it a proven fact that Betelgeuse is about 640 ly away? Why is Stellarium so imprecise?
Rob Jeffries' comment below and this link answer my question well, rather than the link provided above.


texts: Which 16 antenna locations were used this MeerKAT radio image?

texts:
The final configuration of the MeerKAT radio array will be 64 dishes. In the press release of July 16, 2016 a radio image is shown using a completed sub-set of 16 dishes.

Which 16 are these? I can find documents on-line with coordinates for 64 location, (sometimes numbered 1 through 64, but not here), but I can't figure out which 16 are used to produce this image.

I found images of KAT-7 and MeerKAT in google maps - maybe someday we can get daily ground truth updates from Planet Labs, but for right now I'll stick to stackexchange.

Image from the press release:

Above: MeerKAT array core from Google Maps at (30.7136109S, 21.4399576E). The remaining sites are farther away and can be seen if one zooms out.

Above: KAT-7 array from Google Maps at (30.7217011S, 21.4070518E)


texts: Lack of objects between heliopause and Oort cloud?

texts:
If we take a look at a logarithmic scale of the Solar System, there appears to be a large gap between the heliopause and the Oort cloud:

Why is that? There are some objects in the gap, but why are most of the Oort cloud objects in one area? Shouldn't it also fill the large gap in the picture just as much?


texts: What causes objects to become tidally locked?

texts:
I'm trying to write a gravity simulation (suns planets etc), and was hoping tidal locking could be one feature demonstrated.

Using a simple equation for gravity has produced some interesting results, but (unless its emergent behaviour) I see nothing that would encourage tidal locking. But, after some reading it appears tidal locking is quite common, planets and their satellites, planets and suns, suns and other suns (binary stars).

Is it a result of the formation stage of these objects, or is it somehow a function of the equation of gravity?


texts: What are the pros and cons of angular cross-correlation in real space and harmonic space?

texts:
In observational cosmology people often measure and model cross-correlations between different tracer maps. There are generally two ways to measure cross-correlations:

in real space (two-point function):

$$
\xi^{uv}(\theta) \equiv \left\langle  u(\boldsymbol{\theta'}) v(\boldsymbol{\theta'}+\boldsymbol{\theta}) \right\rangle_{\boldsymbol{\theta}'}
$$

in harmonic space (angular power spectrum)

$$
\xi^{uv}(\theta)=\int d \ell \frac{\ell}{2 \pi} C_{\ell}^{uv} J_{0}(\ell \theta)
$$
I'm wondering in the sense of measurements, modelling, systematics, etc, what are the pros and cons of these two methods?


texts: Why don't planets and asteroids have (cometary) tails?

texts: Comets have tails. We all know that, and a lucky few have seen the better known. So why don't the planets (e.g. Earth, Mars) have tails? Why don't asteroids don't have tails?


texts: Do the earth and the moon reflect the different fractions of total solar radiation proportionally?

texts:
Reading on this website that: "All of the energy from the Sun that reaches the Earth arrives as solar radiation". "Solar radiation includes visible light, ultraviolet light, infrared, radio waves, X-rays, and gamma rays".
Here Albedo is explained to refering to the entire spectrum of solar radiation.
The earth and the moon obviously reflect different amounts of total solar radiation, but question is if they reflect the different solar radiation fractions proportionally?
(Proportional reflection is when all the different light spectrum fractions increases, or decreases, with the same percentages.)
Or do earth and/or moon reflect light dis-proportionally?
Rephrasing the question:
We know how much the difference in visible geometric albedo between earth and the moon
is, but is that figure the same when comparing  reflection of infrared, or any of the other parts of the light spectrum?


texts: What new instruments "so sensitive that we can see (large circumgalactic winds) have only been on telescopes for a few years"?

texts:
The Rhodes College press release Prof. David Rupke and Team of Astrophysicists Make Major New Discovery About Galaxy Evolution links to

Astronomy Community/Nature.com: The Making of Makani; The story of how we encountered an enormous galactic wind surrounding the Makani galaxy illuminates the scientific process of discovery and collaboration.
Vimeo: Makani 360-degree rotation of KCWI spectral cube

and references the new Nature paper A 100-kiloparsec wind feeding the circumgalactic medium of a massive compact galaxy (viewable in  arXiv)
and includes the video below, in which Prof. Rupke says near the end after about 03:43:

While I’m hopeful that it’s the tip of the iceberg, and that we will find many other galaxies in which we see these large winds extending into the circum-galactic medium, but of course we have to go out and look.
These new instruments that are so sensitive that we can see these things have only been on telescopes for a few years.
There’s more galaxies that we haven’t looked at than we have.

The last sentence (taken by itself) is probably an understatement :-)
Question: What "...new instruments so sensitive that we can see these things have only been on telescopes for a few years"? I'm guessing that "instruments on telescopes" means these are image sensors or imaging spectrometers on visible or IR telescopes on the ground, and not related to radio telescopes, but that's just a guess.

Figure 1 The giant galactic wind surrounding the massive, compact galaxy Makani, observed by emission from the [O II] line at λ=3726 A and 3729 A. The colour scale and white contours show observed-frame surface brightness, and the axes are labeled in kiloparsecs from the galaxy nucleus. Contours are 2–16% of peak flux, spaced by factors of 2. A rest-frame V-band image of the galaxy (Hubble Space Telescope/WFC3 F814W filter) is superimposed on the center of the [O II] image taken with KCWI at the Keck II telescope. The small circle at the centre illustrates the radius of the compact core (400 pc). North is up and east is to the left.


texts: What are the procedures and protocols to use with Gauss'method and personal observations?

texts:
I would like to use the Gauss' method to determine the orbit of planets of solar system.

I would like to calculate their orbits with personal observations.

What is the methodology/procedure/protocol to follow?

What data do I need to measure during my observations?


texts: How certain are we about the universe's flatness?

texts:
The universe is thought to be flat: $\Omega = 1 \pm 1\%$. As I understand it we can determine this by measuring triangles against the CMB.

Yet during inflation dark energy made the universe grew much larger than the radiation universe, of which the CMB is the limit. Isn't it possible then that at the "smaller" scale of our visible universe it appears flat, but at the universe's full size it's curved? A bit like a square of 1 meter sides on the surface of the earth also looks flat, while at larger scale the earth is curved.

What are the chances that the 1% uncertainty could lead us to a universe with $\Omega \ne 1$?


texts: Semi-major axis vs. apogee and perigee of orbit

texts:
This article on Wikipedia about Sedna states that its aphelion is 937 AU, its perihelion is 76 AU and its semi-major axis is 484 AU.
I would have expected the SMA to be half of the sum of the aphelion and perihelion. Is the article in error, or is there a difference that I'm not aware of?
I know apoapsis and periapsis are sometimes given relative the surface of the object being orbited, see this thread, but the effect should be negligible in this case and would anyway work in the opposite direction. Anything else I'm not seeing?


texts: How to estimate uncertainty of measurements of equivalent widths?

texts:
I'm measuring equivalent widths of absorption lines using a spectrum of a star. I make two or three measurements of each line by making reasonable gaussian fits of the line with IRAF's splot tool. Then I calculate the mean of the measurements, which serves as my final equivalent width estimate.

What is a good way of estimating the uncertainty of this measurement?

My current method

I'm currently using half of the range for the uncertainty. For example, if I made two measurements 10 and 16 mA (milliangstrom), then the mean is 13 mA and uncertainty is 3 mA. This gives the estimate of equivalent width to be 13±3 mA. Do you see any problems with this method of estimating uncertainty?


texts: How do CMB photons 'gain energy when they pass through normal regions of space with matter' and 'lose energy when they pass through voids'?

texts:
The Space.com article Huge Hole Found in the Universe says:

The gargantuan hole was found by examining observations made using the Very Large Array (VLA) radio telescope, funded by the National Science Foundation.
There is a "remarkable drop in the number of galaxies" in a region of sky in the constellation Eridanus, Rudnick said.
The region had been previously been dubbed the "WMAP Cold Spot," because it stood out in a map of the Cosmic Microwave Background (CMB) radiation made by NASA's Wilkinson Microwave Anisotopy Probe (WMAP) satellite. The CMB is an imprint of radiation left from the Big Bang, the theoretical beginning of the universe.
"Although our surprising results need independent confirmation, the slightly colder temperature of the CMB in this region appears to be caused by a huge hole devoid of nearly all matter roughly 6 to 10 billion light-years from Earth," Rudnick said.
Photons of the CMB gain a small amount of energy when they pass through normal regions of space with matter, the researchers explained. But when the CMB passes through a void, the photons lose energy, making the CMB from that part of the sky appear cooler. (emphasis added)

Question: How do CMB photons gain energy when they pass through "normal regions of space with matter" and lose energy when they pass through voids?


texts: Can somebody explain heisenberg uncertainty principle to 14 year old me?

texts: I'm a young student that's very curious about physics and especially some physics theories. I've watched a TED video about the Heisenberg uncertainty principle, but I couldn't fully understand it and I'm looking for a fairly easy explanation if possible.


texts: How does the Moon look like from different latitudes of the Earth?

texts:
I have heard, that on the northern hemisphere, you can estimate a direction of south if you imagine a line going through the tips of the border between illuminated and shadowed part of the Moon, and where this line crosses the horizon, that is estimated direction of the south (and vice versa from the southern hemisphere).

This inspired me to think about how much information could one get simply by observing the Moon. I think you can estimate the latitude of your location. I live in the northern hemisphere and never have been anywhere else, so it's all just an imagination. That's why I need somebody to confirm or correct my conclusions.

I think the angle of the tilt of the Moon will be different as seen from different latitudes. Specificaly near the poles you would see the line between illuminated and shadowed part of the Moon very verticaly. At the equator horizontaly. And somewhere in the middle between the equator and the pole tilted under some angle.

You would also see the Moon much lower on the horizon when standing near the poles and going near the zenith when standing on equator.

I also think you can use observation of the phase changes througout a month to find out whether you are at the southern or the northern hemisphere.

So this is what I imagine the Moon looks like. I have searched the internet for relevant information, but nobody seems to discuss the whole thing in detail. There is only one picture somewhat depicting the tilt of the Moon as seen from 3 different latitudes of the Earth and that's it.

EDIT
A software for simulation of the skies (Stellarium) have been recommended to me by @barrycarter and after few hours playing with it, I can clonclude, that the graphics I provided above are accurate.

An interesting observation made while seeing the Moon during daytime. In the real life at the surface of the Earth this observation would not be possible, but the software allows it. Since the Sun is no longer positioned "under horizon", it illuminates the Moon from different angle, than depicted in the grapics.

I made few screeenshots from view from the France (northern hemisphere) of this situation to illustrate what I mean.

It is possible to see, that at nighttime, the moon looks exactly as in the graphics, but as soon as the Sun rises, the illumination direction changes.


texts: What is the total number of stars in the universe?

texts: I mean a total number of stars, not the only ones that we can see.


texts: Precision of geocentric gravitational constant

texts:
I am looking for an answer as to why the geocentric gravitational constant, μ, defined as the product of the gravitational constant, G, and the mass of a body (earth in this case), M, can be calculated to a higher degree of precision than either G or M alone.

From wikipedia

  ...for celestial bodies such as Earth and the Sun, the value of the product GM is known much more accurately than each factor independently. Indeed, the  limited accuracy available for G limits the accuracy of scientific
   determination of such masses in the first place.

Can someone explain this? I can't find a good answer anywhere I look.


texts: What resources do C-Type(Carbonaceous) Asteroids contain?

texts: What resources do C-Type asteroids contain? The research I've done has come up with carbon, but what form is the carbon in? Graphite, diamonds, coal, or some other material?


texts:
While looking for a way to prolong an orbit via moon power I was faced with the parameters of what would be a stable orbit by length of time an object stayed in orbit, What is the definition of a stable orbit? Is there a such an orbit since all orbits eventually degrade?

Can the moon's gravity provide enough force to keep an object in Earth's orbit?


texts:
I'm not an astronomer but I enjoy looking up at the sky.

So tonight I saw something moving in the sky. It looked like a star, and it was definitely not a plane (I checked in flightradar).

Is there an app, similar to flightradar for planes, that will tell me what's traveling above me in the sky?


texts:
I was taking an astronomy test, the following question came up:

  The most important function of the astronomical telescope is:

  Resolving power
  Light gathering power
  magnifying power
  focal length

The focal length obviously means nothing here, as well as the magnification (that can always be done later). As far as resolving power and light gathering power go though, they both seem to be "equally" important, in that without the first, there is no detail, and without the second, there is no image.

It does seem that exposure time can compensate for a lack of light gathering power (what matters is the product between the two), but nothing can compensate for resolving power.

My professor seems to think the answer is resolving power. Why is this? Is this some well known idea in astronomy?


texts: How to scale down solar system data to simulatable values

texts:
Okay, I am seriously ashamed for asking this especialy when I geniualy study on physics but there is something that bugs me with the simulation I am working on.
I am re-creating the solar system in an n-body simulation that i programmed before. And I've a problem with scaling down the solar data. So even if I use kg and km for the metric units, the values are far bigger than the variables can hold in programming. Also as some of you know, bigger the value is, bigger the floating point error it makes. (error noise in data) Also it makes it slower to process.
I decided to scale down the data with a reference point, and for that, I took the earth's radius as 1 unit. And scaled down every other distance and radius according to it. (So a unit is 6371 km just to be clear)
But I am not sure whether if I should scale down the mass or not. My common sense says that I should scale down the mass so density of each body should remain same. So I took the density, and calculated a new mass value for each body, with the new scaled down radius.
But I am somehow couldn't conviced myself about If it's true or not. So here I am, asking to you :) Should I also scale down the mass?
PS.1: I used using $F = GMm/r^2$ equation for the calculactions as usual. (Iterating it through each body pairs)
If there are other programmers like me interested in making a simulation like this, how did you accomplish this data size problem? Are there any better solutions than scaling down the values?
PS. I have created an excel file that does the scale conversion. So I am sharing  the sheet in OneDrive. (http://1drv.ms/1NIekGo) If you can check my calculations and values, that I'd also be really helpful to me. Thanks for any help.


texts: Where and how to look up the coordinates and magnitude of the star in this occultation prediction?

texts:
The motivation for this question comes from this question. A star is named in the occultation prediction shown below, from AsteroidOccultations.com's News & Announcements for 2014 MU69 on 2017-Jun-03 03:11.

I believe that the star is in the Omega Centauri cluster, and I believe it is between +12 and +14 visual magnitude roughly. The name given in the prediction is NH -08194514G The location shown in the prediction is R.A: 19 03 34.493 DEC -20 34 39.34 but according to Wikipedia the coordinates of the cluster are roughly R.A. 13h 27m, DEC. -47deg, 29m.

I need help understanding why the two coordinates seem so different (am I misunderstanding the prediction?) and finding out how to look up this particular star’s visual magnitude by using its name. I’ve tried a few quick searches but realized that I was over my head and not likely to get the right information.

From the linked question:

People have fanned out over South America and South Africa with telescopes with cameras and GPS clocks and have attempted to watch the shadow of a roughly magnitude +13 star cast by a rock in the KUIPER BELT pass over the Earth!

Early Twitter reports reported clear skies and images of the Omega Centauri star cluster. There is a Twitter hash tag for these events, #mu69occ. Here is a 500 millisecond exposure from a few days before the occultation. The short exposure time is necessary to resolve small scale debris from the main occultation.

above: Omega Centari Star Cluster, 500 millisecond exposure. Tweeted by Alex Partker.

The goal is actually to look for shadows cast by even smaller debris, orbiting around the rock in the Kuiper belt. This is for New Horizons mission planning.

above: From AsteroidOccultations.com's News & Announcements for 2014 MU69